Built-in containers like dict use an ellipsis to represent a recursive item. In the symbols index, “...” only links to the secondary prompt; I think it should also link to a paragraph explaining the display of recursive containers.

Since the appearance of reprs is not guaranteed. I don't think this should be documented (because doing so makes it a guaranteed behavior). In fact, the appearance has changed over time from ... to [...] in and may change at some point to <...> so that it can't be confused with an actual Ellipsis object. At best this should be a FAQ entry or we can defer to behaviors that are documented and guaranteed (such as reprlib.recursive_repr() and its default fillvalue).
I concur with David Murray that the Ellipsis object should be indexed and cross-referenced.